Add --enable=all to ShellCheck by default

Change enforced shell type from `dash` to `sh` and excluded
`SC2039` and `SC3043` by default. `local` keyword is accepted by all
POSIX shells from practical point of view. There is no need anymore
to enforce dash so `local` is accepted.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #13020

contrib/initramfs/scripts/local-top/Makefile.am

@@ -5,4 +5,3 @@ localtopdir = /usr/share/initramfs-tools/scripts/local-top
 dist_localtop_SCRIPTS = \
         zfs
 
-SHELLCHECK_OPTS = --enable=all